A parallel hybrid driveline may include an engine, a driveline disconnect clutch, and an electric machine. The engine and electric machine may be selectively operated in response to vehicle operating conditions. If the engine is stopped, it may be restarted by the electric machine when the driveline disconnect clutch is closed. However, closing the driveline disconnect clutch to start the engine may cause a torque disturbance in the vehicle driveline because it may be difficult to accurately estimate torque transferred by the driveline disconnect clutch. Additionally, driveline inefficiencies may reduce the vehicle's fuel efficiency if the torque converter clutch is fully open during vehicle launch.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for operating a driveline, comprising: operating an electric machine in a torque control mode in response to a torque converter clutch torque capacity available at a transmission line pressure being greater than a driver demand torque; and operating the electric machine in a speed control mode in response to the torque converter clutch torque capacity available at the transmission line pressure being less than the driver demand torque.
By operating an electric machine in a speed control mode when transmission line pressure is low, it may be possible to reject driveline torque disturbances via the electric machine and deliver a desired driver demand torque. Additionally, by operating the electric machine in a torque control mode when transmission line pressure is higher, it may be possible to lock a torque converter clutch to improve driveline efficiency while providing at least a portion of driver demand torque via the electric machine.
The present description may provide several advantages. In particular, the approach may improve driveline efficiency while providing a desired driver demand torque. Additionally, the approach may improve vehicle drivability via improving vehicle launch. Further still, the approach may improve engine starting.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.